This application is based upon and claims the priority of Japanese Patent Application No. 2001-065935, filed on Mar. 9, 2001, which is hereby incorporated by reference in its entirety.
1. Field of the Invention
The present invention generally relates to an engine for land vehicles. More specifically, the present invention relates to an improved engine layout for snowmobiles that results in a smaller overall vehicle body.
2. Description of the Related Art
Snowmobiles are powered by internal combustion engines that are mounted within a substantially enclosed engine compartment forward of the rider""s seat. The engine compartment typically is defined within a cowling and is generally relatively small. Two-cycle engines having a generally transverse orientation have been used in snowmobiles. Such engines generally have a crankshaft, an output shaft and an auxiliary shaft longitudinally spaced from one another. In some configurations, the shafts are arranged in the same horizontal plane such that the shafts are seemingly stacked side-by-side.
Four-cycle engines provide various benefits and are therefore being incorporated into more vehicles. For example, four-cycle engines provide better engine fuel economy and engine control and less exhaust emissions. In order to increase the output power of the four-cycle engine, however, greater piston displacement is often used. This, along with size and location of the valve gear and cam mechanisms, increases the height of the engine, and hence the height of the snowmobile. While the crankshaft, output shaft, and auxiliary shaft could be lowered to counteract the increased height of the snowmobile, the shafts would then interfere with the steering mechanisms associated with the front skis.
Thus, a four-cycle engine layout that can reduce the engine compartment volume needed to house the engine is desired. Additionally, the engine layout preferably lowers the center of gravity of the engine, while remaining simply constructed.
Accordingly, one aspect of the present invention involves a snowmobile that includes a frame assembly that has a longitudinal axis. An internal combustion engine is mounted generally transversely to the frame assembly. The snowmobile also has a steering linkage mounted to the frame assembly. The engine includes a cylinder bore and a piston reciprocally positioned in the cylinder bore. The piston drives a crankshaft of the engine. The crankshaft is mounted in a crankcase that has a vertical transverse center plane. The crankshaft extends along a first axis. The crankshaft is arranged to drive an output shaft that is mounted in the crankcase. The output shaft extending along a second axis that is generally parallel to said first axis. The output shaft is arranged to drive the vehicle through a transmission. The internal combustion engine also includes an auxiliary shaft arranged to drive an oil pump to deliver lubricating oil to at least one component of the engine. The auxiliary shaft extends along a third axis that is generally parallel to said first axis. Two of the first axis, the second axis, and the third axis are disposed in a common plane. The other of the first axis, the second axis, and the third axis is offset from the common plane.
Another aspect of the present invention involves a snowmobile that includes a frame assembly that has a longitudinal axis and an internal combustion engine mounted generally transversely to the frame assembly. The engine includes a cylinder bore and a piston reciprocally positioned in said cylinder bore. The piston drives a crankshaft of the engine that is mounted in a crankcase having a vertical transverse center plane. The crankshaft is drives an output shaft that is mounted in the crankcase. The output shaft drives the vehicle through a transmission. The engine also includes a starter motor and a lubrication system. The lubrication system includes an oil cooler, an oil filter, and an oil pump to deliver lubricating oil to at least one component of the engine. The oil pump and the output shaft are located on one side of the transverse center plane. The oil filter, the oil cooler, and the starter motor are located on the other side of the transverse center plane.
Another aspect of the present invention involves a snowmobile that includes a frame assembly that has a longitudinal axis and an internal combustion engine mounted generally transversely to the frame assembly. The engine includes a cylinder bore and a piston reciprocally positioned in the cylinder bore. The piston drives a crankshaft of the engine. The crankshaft is mounted in a crankcase having a vertical transverse center plane. The crankshaft comprises at least one crank web and driving a drive gear. The crankshaft is mounted in a crankcase that has a vertical transverse center plane. The crankshaft is arranged to drive an output shaft through the drive gear, the output shaft being mounted in the crankcase. A driven gear mounted on said output shaft is driven by the drive gear. The engine also comprises a damper mounted on said output shaft and a valvetrain. The valvetrain includes a flexible transmitter that causes a plurality of valves to be actuated. The damper is positioned between said drive gear and said crank web. The damper is also located at least partially positioned in a plane that is normal to an axis of rotation of the crankshaft and that includes a portion of the flexible transmitter.